Senior Software Engineer (Telco & Comms)

Russian hacker, Vladimir Leonidovitch Levin, attempted the biggest bank heist the world had ever seen via dial-up internet in 1994, Zia Hayat, Callsign CEO and founder, was hooked - armchair fraud became a real possibility. From this moment, Zia knew he wanted to play a part in stopping the bad guys and securing the internet for all. Founded In 2012, Callsign's mission has been to make Digital Identity simple and secure for everyone and everything. In that time, we've grown to over 200 employees, opened offices in Singapore and Abu Dhabi, been recognised as a WEF Global Innovator and our technology is being used by many of the world's leading financial institutions to keep millions of consumers safe.

But we aren't stopping here. The identity revolution has only just begun, and we are looking to hire the brightest and inquisitive minds to help us make every web, mobile and physical Interaction seamless and secure. If this sounds like you, lets chat.

• →Write production-ready code, and know the pipeline and the chart that ship it.
• →Write low-level designs another engineer can build from, and represent the team in architecture reviews.
• →Threat-model each feature, and design authentication, authorization, and data handling in from the start.
• →Instrument before release, take a turn on call, and drive faults to a root cause.
• →Find technical gaps early, propose each fix with a cost and a benefit, and use AI tooling.
• →Mentor engineers, hold the standard on tests and error handling, and interview candidates.

• 8+ years with Java 17+, Spring Boot, and Spring Security, debugging JVM and Spring issues from thread dumps, heap dumps, and traces.
• Designs and operates microservices for client traffic, with API versioning and testing across unit, integration, contract, and load.
• Designs for failure and scale: idempotency, retries, circuit breakers, and caching. Diagnoses bottlenecks with data.
• Strong relational data modeling and query design, primarily in MySQL, with schema and index tuning proven under load.
• Treats security as a design input: OWASP Top 10, authentication and authorization, secrets management, and data handling.
• Writes designs other engineers can build from, and reviews peers' designs.
• Deploys and runs services on Kubernetes with Docker, Helm, AWS, and CI/CD, and debugs failed deployments from the chart or pipeline.
• Owns a change from design through on-call, and instruments it so a fault shows before a client reports it.

• Reactive Java in production: Spring WebFlux, Project Reactor, RxJava, or Vert.x.
• MNO and telco integrations: number insight, SIM swap, and other network signals.
• Authentication and authorization standards: OAuth 2.0, JWT, SAML, FIDO, or WebAuthn.
• Has shipped into banking, payments, or another regulated industry, and has faced an audit or client security review.
• Runs services against contractual uptime commitments: SLIs, SLOs, and error budgets.
• Runs Kafka in production, and has diagnosed consumer lag or rebalance issues.
• Manages infrastructure as code with Terraform.